Adverse drug reactions represent a partly preventable cause of morbidity. Computer-based tools may be useful for the prevention of those events resulting from drug interactions. While several such tools are currently available to practitioners, they have rarely been compared regarding their performances and limits. This article presents a benchmark evaluation of seven drug interaction databases which may be elected by physicians or pharmacists as an aid to prescription on a regular basis. None of the databases tested appears to be perfect, and the systems vary in their overall completeness and ease of use.